Sodium hydroxide (NaOH), CAS 1310-73-2, also known as lye or caustic soda, is an inorganic compound industrially produced as a 50% solution by the electrolytic chloralkali process in which chlorine gas is also produced. Evaporation of water from this solution yields white crystalline solid sodium hydroxide that readily absorbs moisture from air. Sodium hydroxide dissolves in water to form a colorless solution.